When it comes to the selection of a water treatment technique for treating an organic wastewater, it is important to take the characteristics of substrates and contaminants relating to the organic wastewater treatment into consideration so as to find a technically effective and economically feasible wastewater treatment method specifically for treating such organic wastewater. Wastewater treatment can be a multi-stage process to renovate wastewater before it reenters a body of water. The goal is to reduce or remove organic matter, solids, nutrients, disease-causing organisms and other pollutants from wastewater, which can include the following processes: (1) biological treatment, such as bacterial decomposition; (2) chemical treatment, such as chemical oxidation and chemical precipitation; (3) thermal treatment, such as incineration and plasma treatment; (4) physical treatment, such as filtration and separation. Moreover, the first three processes are capable of converting the organic compounds in the wastewater into non-toxic compounds that can be easily decomposed, or breaking down the same completely into inorganic compounds, carbon dioxide and water, which are exemplified by the wet oxidation method, supercritical water oxidation method and Fenton's oxidation method shown respectively in U.S. Pat. No. 5,820,731, U.S. Pat. No. 6,010,632, U.S. Pat. No. 4,604,214. The aforesaid method are advantageous in that: they are capable of effectively breaking down the organic pollutants into carbon dioxide, water and other compounds of low molecular weight such as acids or simple hydrocarbons, through the oxidation effect induced by high temperature and high pressure or by hydroxyl (OH) free radicals. However, it is important to design a process for removing the chemical reagents added in the wastewater during the performing of the aforesaid methods so as to prevent the generation of some organic compounds of higher toxicity during the breaking down of the original organic pollutants in the wastewater and therefore cause the generation of so-called secondary waste effluent.
As for the aforesaid physical treatment, it is performed by the use of a filtration means to screen and separate those toxic organic solids from the wastewater so as to purify the same for discharging, in that there is no chemical change in the structures of the toxic organic solids. There are already many such physical treatments currently available, such as those disclosed in U.S. Pat. No. 6,319,412 and U.S. Pat. No. 6,379,555, which uses an activated carbon disposed on a fixed bed for absorbing the organic solids suspended in the wastewater for preparing the same for the other subsequent processes. The aforesaid physical treatment is advantageous in that: there will be no secondary waste effluent problem since there has no chemicals being added into the wastewater during the process, and moreover, the concentration or sludge resulting from the physical treatment can further be processed by an incineration procedure or solidification procedure as its volume is greatly reduced comparing with the original wastewater.
Recently, with the rapid advance of technology, there are more and more different industrial wastewaters being generated from the manufacturing processes of different industries, which might be composed of many complex compounds that are not biodegradable and thus can not be treated by a simple one-stage process. Moreover, when the wastewater is composed of various high boiling-point organic compounds with high water content, it is difficult to be treated by the simple one-stage process. In the current high-tech industries such as the semiconductor fabrication industry, there are various industrial wastewaters being generated in its manufacturing process, such as those wastewaters generated from the wafer cleaning process, the photoresist removal process, the wet etching process, the abrasion process, the cutting process, or the absorbent regeneration process, and so on. Taking the condensation/absorbent regeneration wastewater generated from the volatile organic compound (VOC) exhaust gas treatment facility in the photoresist removal process, such regeneration wastewater, being mainly composed of certain high boiling-point organic solvents, such as dimethyl sulfoxide (DMSO), monoethanol amine (MEA), N-methyl pyrrolidone (NMP), etc; and a little low boiling-point organic solvent, such as acetone, has a total carbon concentration (TOC) ranged between 8000 mg/L to 16000 mg/L. It is noted that such regeneration wastewater is usually being processed by a means of incineration, but since it's water content is usually higher than 90%, the burning of such regeneration wastewater not only is not energy efficient, but also may cause a great amount of carbon dioxide to be emitted into atmosphere and thus cause another environmental issue.
Taking another kind of wastewater generated from the cleaning of a plastic pipe after it is being processed by a thermal treatment as it is being fabricated, such wastewater will contains ethylene glycol with an average concentration of 0.06M as ethylene glycol whose boiling point is 197.6° C. is used as the heat medium in the thermal treatment. It is noted that the aforesaid wastewater is also high in water content and thus it is not cost efficient to process the same by means of incineration. Nevertheless, considering the long hours of time required for the cultivation and growing of microorganisms used for processing the aforesaid wastewater in a biological manner, it is not feasible to perform a biological treatment upon the aforesaid wastewater, not to mention that the biochemical oxygen demand (BOD) of aforesaid wastewater after being processed by biological treatment usually will excess the standard specified in the environmental regulations.
There are already many prior arts trying to process various organic wastewaters in a multi-stage manner. First, the wastewater is distilled while accumulating and storing the distilled liquid in a storage tank. Next, as the distilled liquid still contain many organic compounds whose concentration is not conform with the environmental standard for discharging, the distilled liquid will be further processed by another treatment, such as a secondary distillation or a UV/O3 treatment, for enabling the TOC of the distilled liquid to drop and thus conform with the environmental standard for discharging. Although the aforesaid multi-stage process is able to reduce the TOC of the wastewater for enabling the same to conform with the environmental standard for discharging, it is sill not feasible since not only it is not energy efficient as it will require to distill the wastewater multiple times, but also it is not economically sound as the UV/O3 treatment or biological treatment is a long-hour treatment that can only be performed with some expensive equipments.
Therefore, it is required to have a low-cost, high-efficient wastewater treatment apparatus and method with much less complicated processes that can be easily adapted for various industries.